Re: Finding only the real roots

*To*: mathgroup at smc.vnet.net*Subject*: [mg113635] Re: Finding only the real roots*From*: Alexei Boulbitch <alexei.boulbitch at iee.lu>*Date*: Fri, 5 Nov 2010 05:13:29 -0500 (EST)

Hi, Peter, All your questions have simple answers, but first your should write down correct Mathematica expressions. NSolve, rather than Nsolve, Sqrt, rather than root and [] at Sqrt, rather than () at root. You will hardly move further without learning few basic things about Mathematica, so do it. In particular, NSolve[1/2 + c + g (1 - p) + Sqrt[c + p*g - 1] == 0, p] {{p -> (0.125 (-1. (-8. - 8. c - 8. g) g - 11.3137 Sqrt[-0.125 g^2 + 1. c g^2 + 0.5 g^3]))/g^2}, {p -> ( 0.125 (-1. (-8. - 8. c - 8. g) g + 11.3137 Sqrt[-0.125 g^2 + 1. c g^2 + 0.5 g^3]))/g^2}} but I would do Solve[1/2 + c + g (1 - p) + Sqrt[c + p*g - 1] == 0, p] {{p -> (2 g + 2 c g + 2 g^2 - Sqrt[-g^2 + 8 c g^2 + 4 g^3])/( 2 g^2)}, {p -> ( 2 g + 2 c g + 2 g^2 + Sqrt[-g^2 + 8 c g^2 + 4 g^3])/(2 g^2)}} instead. Also Manipulate works. Try this for instance: Manipulate[ Solve[1/2 + c + g (1 - p) + Sqrt[c + p*g - 1] == 0, p], {c, 0, 1}, {g, 0, 1}] Have fun, Alexei Hi all, I'm trying to numerically evaluate a function using NSolve, for example Nsolve[1/2+c+g(1-p)+root(c+p*g-1)==0,p] where my two variables g and c are both in the interval [0,1]. But, since the root is not always positive I do not get a solution to NSolve. The idea was therefore to first define the positive roots and then to do NSolve. My questions are therefore; 1) Is this the best approach, or are there more direct ways? 2) What should I do to only get the real roots? 3) If I first solve the root, and then use NSolve, will I still be able to use functions such as Manipulate on the NSolve solution? Best, Petter -- Alexei Boulbitch, Dr. habil. Senior Scientist Material Development IEE S.A. ZAE Weiergewan 11, rue Edmond Reuter L-5326 CONTERN Luxembourg Tel: +352 2454 2566 Fax: +352 2454 3566 Mobile: +49 (0) 151 52 40 66 44 e-mail: alexei.boulbitch at iee.lu www.iee.lu -- This e-mail may contain trade secrets or privileged, undisclosed or otherwise confidential information. If you are not the intended recipient and have received this e-mail in error, you are hereby notified that any review, copying or distribution of it is strictly prohibited. Please inform us immediately and destroy the original transmittal from your system. Thank you for your co-operation.